I've never heard of getting them professionally serviced. I just seafoamed not too long ago. 1/3 can in the gas tank (along with 1/3 in the crankcase and 1/3 in the brake booster) will clean out your entire fuel system. Also change your plugs and oil within 100 miles of seafoaming.
You can send them off to be pressure tested and serviced. It definitely can't hurt performance or fuel economy. It all depends on how much you're willing to spend and if you can deal with the down time.
On car services offered by lube shops don't do anything you can't do yourself.
It's one of those things that if they work, you won't gain anything. If there's something wrong with them, you'll benefit. Like the fuel filter, in a perfect world it should never need to be changed but one tank of gunk can make a real mess.
I don't believe in fixing things that aren't broken. If it's running okay, don't touch it. There are better things to spend money on. I have 198000 miles on mine with no intention of cleaning the injectors.
